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Date: Wed, 26 Nov 2014 23:20:38 +0200
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Willem de Bruijn <willemb@...gle.com>
Cc: Network Development <netdev@...r.kernel.org>,
David Miller <davem@...emloft.net>,
Eric Dumazet <eric.dumazet@...il.com>,
Daniel Borkmann <dborkman@...hat.com>
Subject: Re: [PATCH rfc] packet: zerocopy packet_snd
On Wed, Nov 26, 2014 at 02:59:34PM -0500, Willem de Bruijn wrote:
> > The main problem with zero copy ATM is with queueing disciplines
> > which might keep the socket around essentially forever.
> > The case was described here:
> > https://lkml.org/lkml/2014/1/17/105
> > and of course this will make it more serious now that
> > more applications will be able to do this, so
> > chances that an administrator enables this
> > are higher.
>
> The denial of service issue raised there, that a single queue can
> block an entire virtio-net device, is less problematic in the case of
> packet sockets. A socket can run out of sk_wmem_alloc, but a prudent
> application can increase the limit or use separate sockets for
> separate flows.
Sounds like this interface is very hard to use correctly.
> > One possible solution is some kind of timer orphaning frags
> > for skbs that have been around for too long.
>
> Perhaps this can be approximated without an explicit timer by calling
> skb_copy_ubufs on enqueue whenever qlen exceeds a threshold value?
Not sure. I'll have to see that patch to judge.
> >
> >> ---
> >> include/linux/skbuff.h | 1 +
> >> include/linux/socket.h | 1 +
> >> include/uapi/linux/errqueue.h | 1 +
> >> net/packet/af_packet.c | 110 ++++++++++++++++++++++++++++++++++++++----
> >> 4 files changed, 103 insertions(+), 10 deletions(-)
> >>
> >> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> >> index 78c299f..8e661d2 100644
> >> --- a/include/linux/skbuff.h
> >> +++ b/include/linux/skbuff.h
> >> @@ -295,6 +295,7 @@ struct ubuf_info {
> >> void (*callback)(struct ubuf_info *, bool zerocopy_success);
> >> void *ctx;
> >> unsigned long desc;
> >> + void *callback_priv;
> >> };
> >>
> >> /* This data is invariant across clones and lives at
> >> diff --git a/include/linux/socket.h b/include/linux/socket.h
> >> index de52228..0a2e0ea 100644
> >> --- a/include/linux/socket.h
> >> +++ b/include/linux/socket.h
> >> @@ -265,6 +265,7 @@ struct ucred {
> >> #define MSG_SENDPAGE_NOTLAST 0x20000 /* sendpage() internal : not the last page */
> >> #define MSG_EOF MSG_FIN
> >>
> >> +#define MSG_ZEROCOPY 0x4000000 /* Pin user pages */
> >> #define MSG_FASTOPEN 0x20000000 /* Send data in TCP SYN */
> >> #define MSG_CMSG_CLOEXEC 0x40000000 /* Set close_on_exec for file
> >> descriptor received through
> >> diff --git a/include/uapi/linux/errqueue.h b/include/uapi/linux/errqueue.h
> >> index 07bdce1..61bf318 100644
> >> --- a/include/uapi/linux/errqueue.h
> >> +++ b/include/uapi/linux/errqueue.h
> >> @@ -19,6 +19,7 @@ struct sock_extended_err {
> >> #define SO_EE_ORIGIN_ICMP6 3
> >> #define SO_EE_ORIGIN_TXSTATUS 4
> >> #define SO_EE_ORIGIN_TIMESTAMPING SO_EE_ORIGIN_TXSTATUS
> >> +#define SO_EE_ORIGIN_UPAGE 5
> >>
> >> #define SO_EE_OFFENDER(ee) ((struct sockaddr*)((ee)+1))
> >>
> >> diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
> >> index 58af5802..367c23a 100644
> >> --- a/net/packet/af_packet.c
> >> +++ b/net/packet/af_packet.c
> >> @@ -2370,28 +2370,112 @@ out:
> >>
> >> static struct sk_buff *packet_alloc_skb(struct sock *sk, size_t prepad,
> >> size_t reserve, size_t len,
> >> - size_t linear, int noblock,
> >> + size_t linear, int flags,
> >> int *err)
> >> {
> >> struct sk_buff *skb;
> >> + size_t data_len;
> >>
> >> - /* Under a page? Don't bother with paged skb. */
> >> - if (prepad + len < PAGE_SIZE || !linear)
> >> - linear = len;
> >> + if (flags & MSG_ZEROCOPY) {
> >> + /* Minimize linear, but respect header lower bound */
> >> + linear = min(len, max_t(size_t, linear, MAX_HEADER));
> >> + data_len = 0;
> >> + } else {
> >> + /* Under a page? Don't bother with paged skb. */
> >> + if (prepad + len < PAGE_SIZE || !linear)
> >> + linear = len;
> >> + data_len = len - linear;
> >> + }
> >>
> >> - skb = sock_alloc_send_pskb(sk, prepad + linear, len - linear, noblock,
> >> - err, 0);
> >> + skb = sock_alloc_send_pskb(sk, prepad + linear, data_len,
> >> + flags & MSG_DONTWAIT, err, 0);
> >> if (!skb)
> >> return NULL;
> >>
> >> skb_reserve(skb, reserve);
> >> skb_put(skb, linear);
> >> - skb->data_len = len - linear;
> >> - skb->len += len - linear;
> >> + skb->data_len = data_len;
> >> + skb->len += data_len;
> >>
> >> return skb;
> >> }
> >>
> >> +/* release zerocopy resources and avoid destructor callback on kfree */
> >> +static void packet_snd_zerocopy_free(struct sk_buff *skb)
> >> +{
> >> + struct ubuf_info *uarg = skb_shinfo(skb)->destructor_arg;
> >> +
> >> + if (uarg) {
> >> + kfree_skb(uarg->callback_priv);
> >> + sock_put((struct sock *) uarg->ctx);
> >> + kfree(uarg);
> >> +
> >> + skb_shinfo(skb)->destructor_arg = NULL;
> >> + skb_shinfo(skb)->tx_flags &= ~SKBTX_DEV_ZEROCOPY;
> >> + }
> >> +}
> >> +
> >> +static void packet_snd_zerocopy_callback(struct ubuf_info *uarg,
> >> + bool zerocopy_success)
> >> +{
> >> + struct sk_buff *err_skb;
> >> + struct sock *err_sk;
> >> + struct sock_exterr_skb *serr;
> >> +
> >> + err_sk = uarg->ctx;
> >> + err_skb = uarg->callback_priv;
> >> +
> >> + serr = SKB_EXT_ERR(err_skb);
> >> + memset(serr, 0, sizeof(*serr));
> >> + serr->ee.ee_errno = ENOMSG;
> >> + serr->ee.ee_origin = SO_EE_ORIGIN_UPAGE;
> >> + serr->ee.ee_data = uarg->desc & 0xFFFFFFFF;
> >> + serr->ee.ee_info = ((u64) uarg->desc) >> 32;
> >> + if (sock_queue_err_skb(err_sk, err_skb))
> >> + kfree_skb(err_skb);
> >> +
> >> + kfree(uarg);
> >> + sock_put(err_sk);
> >> +}
> >> +
> >> +static int packet_zerocopy_sg_from_iovec(struct sk_buff *skb,
> >> + struct msghdr *msg)
> >> +{
> >> + struct ubuf_info *uarg = NULL;
> >> + int ret;
> >> +
> >> + if (iov_pages(msg->msg_iov, 0, msg->msg_iovlen) > MAX_SKB_FRAGS)
> >> + return -EMSGSIZE;
> >> +
> >> + uarg = kzalloc(sizeof(*uarg), GFP_KERNEL);
> >> + if (!uarg)
> >> + return -ENOMEM;
> >> +
> >> + uarg->callback_priv = alloc_skb(0, GFP_KERNEL);
> >> + if (!uarg->callback_priv) {
> >> + kfree(uarg);
> >> + return -ENOMEM;
> >> + }
> >> +
> >> + ret = zerocopy_sg_from_iovec(skb, msg->msg_iov, 0, msg->msg_iovlen);
> >> + if (ret) {
> >> + kfree_skb(uarg->callback_priv);
> >> + kfree(uarg);
> >> + return -EIO;
> >> + }
> >> +
> >> + sock_hold(skb->sk);
> >> + uarg->ctx = skb->sk;
> >> + uarg->callback = packet_snd_zerocopy_callback;
> >> + uarg->desc = (unsigned long) msg->msg_iov[0].iov_base;
> >> +
> >> + skb_shinfo(skb)->destructor_arg = uarg;
> >> + skb_shinfo(skb)->tx_flags |= SKBTX_DEV_ZEROCOPY;
> >> + skb_shinfo(skb)->tx_flags |= SKBTX_SHARED_FRAG;
> >> +
> >> + return 0;
> >> +}
> >> +
> >> static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
> >> {
> >> struct sock *sk = sock->sk;
> >> @@ -2408,6 +2492,7 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
> >> unsigned short gso_type = 0;
> >> int hlen, tlen;
> >> int extra_len = 0;
> >> + bool zerocopy = msg->msg_flags & MSG_ZEROCOPY;
> >>
> >> /*
> >> * Get and verify the address.
> >> @@ -2501,7 +2586,7 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
> >> hlen = LL_RESERVED_SPACE(dev);
> >> tlen = dev->needed_tailroom;
> >> skb = packet_alloc_skb(sk, hlen + tlen, hlen, len, vnet_hdr.hdr_len,
> >> - msg->msg_flags & MSG_DONTWAIT, &err);
> >> + msg->msg_flags, &err);
> >> if (skb == NULL)
> >> goto out_unlock;
> >>
> >> @@ -2518,7 +2603,11 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
> >> }
> >>
> >> /* Returns -EFAULT on error */
> >> - err = skb_copy_datagram_from_iovec(skb, offset, msg->msg_iov, 0, len);
> >> + if (zerocopy)
> >> + err = packet_zerocopy_sg_from_iovec(skb, msg);
> >> + else
> >> + err = skb_copy_datagram_from_iovec(skb, offset, msg->msg_iov,
> >> + 0, len);
> >> if (err)
> >> goto out_free;
> >>
> >> @@ -2578,6 +2667,7 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
> >> return len;
> >>
> >> out_free:
> >> + packet_snd_zerocopy_free(skb);
> >> kfree_skb(skb);
> >> out_unlock:
> >> if (dev)
> >> --
> >> 2.1.0.rc2.206.gedb03e5
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